Examination of possibly induced seismicity from hydraulic fracturing in the Eola field, Garvin County, Oklahoma

Examination
of
Possibly
Induced
Seismicity
from
Hydraulic
Fracturing
in
the
Eola
Field,
Garvin
County,
Oklahoma
Austin
Holland
Oklahoma
Geological
Survey
Open-­‐File
Report
OF1-­‐2011
OKLAHOMA
GEOLOGICAL
SURVEY
Open-­���file
Report
Disclaimer
This
Open-­‐file
Report
is
intended
to
make
the
results
of
research
available
at
the
earliest
possible
date
and
not
intended
to
represent
the
final
or
formal
publication.
The
report
is
an
unedited
copy
prepared
by
the
author.
Examination
of
Possibly
Induced
Seismicity
from
Hydraulic
Fracturing
in
the
Eola
Field,
Garvin
County,
Oklahoma
Austin
A.
Holland
Oklahoma
Geological
Survey
Sarkeys
Energy
Center
100
East
Boyd
St.,
Rm.
N-­‐131
Norman,
Oklahoma
73019-­‐0628
August
2011
Oklahoma
Geological
Survey
Open-­‐File
Report
OF1-­‐2011
1
Summary
On
January
18,
2011,
The
Oklahoma
Geological
Survey
(OGS)
received
a
phone
call
from
a
resident
living
south
of
Elmore
City,
in
Garvin
County,
Oklahoma,
that
reported
feeling
several
earthquakes
throughout
the
night.
The
reporting
local
resident
had
also
offered
that
there
was
an
active
hydraulic
fracturing
project
occurring
nearby.
Upon
examination
there
were
nearly
50
earthquakes,
which
occurred
during
that
time.
After
analyzing
the
data
there
were
43
earthquakes
large
enough
to
be
located,
which
from
the
character
of
the
seismic
recordings
indicate
that
they
are
both
shallow
and
unique.
The
earthquakes
range
in
magnitude
from
1.0
to
2.8
Md
and
the
majority
of
earthquakes
occurred
within
about
24
hours
of
the
first
earthquake.
Careful
attention
and
significant
effort
was
put
into
obtaining
the
most
accurate
locations
possible
and
gaining
a
reasonable
estimate
in
the
error
in
locations.
The
nearest
seismic
station
is
35
km
away
from
where
the
earthquakes
occurred.
Formal
errors
in
location
are
on
the
order
100-­‐500
m
horizontally
and
about
twice
that
for
depth.
Examination
of
different
velocity
models
would
suggest
that
the
uncertainties
in
earthquake
locations
should
be
about
twice
the
formal
uncertainties.
The
majority
of
earthquakes
appear
to
have
occurred
within
about
3.5
km
of
the
well
located
in
the
Eola
Field
of
southern
Garvin
County.
The
Eola
Field
has
many
structures,
which
may
provide
conduits
for
fluid
flow
at
depth.
The
well
is
Picket
Unit
B
well
4-­‐18,
and
about
seven
hours
after
the
first
and
deepest
hydraulic
fracturing
stage
started
the
earthquakes
began
occurring.
It
was
possible
to
model
95%
of
the
earthquakes
in
this
sequence
using
a
simple
pore
pressure
diffusion
model
with
a
permeability
of
about
250
mD
(milliDarcies).
While
this
permeability
may
be
high
it
is
less
than
those
reported
for
highly
fractured
rock.
The
strong
correlation
in
time
and
space
as
well
as
a
reasonable
fit
to
a
physical
model
suggest
that
there
is
a
possibility
these
earthquakes
were
induced
by
hydraulic-­‐fracturing.
However,
the
uncertainties
in
the
data
make
it
impossible
to
say
with
a
high
degree
of
certainty
whether
or
not
these
earthquakes
were
triggered
by
natural
means
or
by
the
nearby
hydraulic-­‐fracturing
operation.
Introduction
On
January
18th,
2011,
a
resident
living
in
south-­‐central
Oklahoma
(Garvin
County),
living
south
of
Elmore
City
contacted
the
Oklahoma
Geological
Survey
(OGS)
to
report
feeling
several
earthquakes
throughout
the
night
with
the
first
occurring
at
approximately
6:10
PM
CST
Jan.
17th
and
another
large
one
at
about
2:50
AM
CST
Jan.
18th.
Upon
examination
there
were
in
fact
earthquakes
in
the
area.
The
resident
also
reported
that
there
was
an
active
hydraulic
fracturing
project
being
conducted
in
a
nearby
well.
Examination
of
the
available
seismic
data,
including
EarthScope
USArray
stations
in
the
region,
quickly
confirmed
that
earthquakes
were
occurring
in
the
area.
At
this
point
the
OGS
contacted
the
Regional
Manager
for
the
Oklahoma
Corporation
Commission,
who
indicated
that
there
was
indeed
fracturing
occurring
at
the
Picket
Unit
B
Well
4-­‐18.
Our
analysis
showed
that
shortly
after
hydraulic
fracturing
began
small
earthquakes
started
occurring,
and
more
than
50
were
identified,
of
which
43
were
large
enough
to
be
located.
Most
of
these
earthquakes
2
occurred
within
a
24-­‐hour
period
after
hydraulic
fracturing
operations
had
ceased.
There
have
been
previous
cases
where
seismologists
have
suggested
a
link
between
hydraulic
fracturing
and
earthquakes,
but
data
was
limited,
so
drawing
a
definitive
conclusions
was
not
possible
for
these
cases.
The
first
case
occurred
in
June1978
in
Carter
and
Love
Counties,
just
south
of
Garvin
County,
with
70
earthquakes
in
6.2
hours.
The
second
case
occurred
in
Love
County
with
90
earthquakes
following
the
first
and
second
hydraulic
fracturing
stages
(Nicholson
and
Wesson,
1990).
Figure
1
-­‐
Earthquakes
from
1897-­‐2010
from
the
OGS
catalog
(red
crosses).
Yellow
triangles
are
seismic
stations
from
the
Earthscope
Transportable
Array;
tan
triangles
are
OGS
seismic
stations.
Faults
are
shown
by
thin
black
lines,
solid
are
faults
mapped
from
a
surface
expression,
dotted
lines
indicate
subsurface
faults
(Northcutt
and
Campbell,
1995).
The
main
movement
on
all
of
these
faults
was
in
the
Pennsylvanian
(Granath,
1989).
Hachured
region
shows
the
location
of
the
Eola
Oil
Field
(Boyd,
2002).
South-­‐central
Oklahoma
has
a
significant
amount
of
historical
seismicity,
and
has
been
one
of
the
most
active
areas
within
Oklahoma
since
1977,
when
an
adequate
seismic
network
was
established.
The
nearest
stations
to
the
earthquakes
were
several
Earthscope
Transportable
Array
(TA)
stations.
Without
the
TA
stations
only
Grady
Carter
Garvin
Love
Stephens
Jefferson
Caddo
McClain
Pontotoc
Murray
Cleveland Pottawatomie
Johnston
Marshall
Seminole
Cotton
Comanche
Canadian Oklahoma
Bryan
Okfuskee
FNO
Y35A
Y34A
X35A
X34A
W35A
W34A
96°45'0"W
96°45'0"W
97°0'0"W
97°0'0"W
97°15'0"W
97°15'0"W
97°30'0"W
97°30'0"W
97°45'0"W
97°45'0"W
98°0'0"W
98°0'0"W
98°15'0"W
98°15'0"W
35°15'0"N 35°15'0"N
35°0'0"N 35°0'0"N
34°45'0"N 34°45'0"N
34°30'0"N 34°30'0"N
34°15'0"N 34°15'0"N
34°0'0"N 34°0'0"N
33°45'0"N 33°45'0"N
0 4 8 16 24 32
Kilometers
3
a
few
of
the
earthquakes
could
possibly
have
been
located
and
the
uncertainties
in
the
hypocentral
locations
would
be
quite
large.
Geologic
Setting
The
Eola
Field
lies
at
the
northern
edge
of
the
Ardmore
Basin
and
the
buried
northwestern
extent
of
the
Arbuckle
Mountains
and
contains
a
highly
folded
and
faulted
thrust
system
(Swesnick
and
Green,
1950;
Harlton,
1964,
Granath,
1989).
In
the
Cambrian
this
area
experienced
significant
rifting
associated
with
the
Southern
Oklahoma
aulacogen
(Keller
et
al.,
1983).
After
the
initial
rifting
the
area
experienced
thermal
subsidence
and
sedimentation
(Granath,
1989).
The
area
continued
to
see
periods
of
subsidence
and
sedimentation
with
a
few
periods
of
erosion
represented
by
unconformities
(Swesnik
and
Green,
1950).
In
the
mid-­‐
Pennsylvanian
the
area
began
to
experience
significant
transpression
associated
with
the
Ouachita
Orogen
(Granath,
1989).
Because
of
the
areas
complex
tectonic
history
it
is
quite
likely
that
the
nature
of
faults
has
changed
through
time
and
that
normal
faults
associated
with
the
aulacogen
and
later
basin
accommodation
were
reactivated
in
the
mid
to
late-­‐Pennsylvanian
with
a
new
sense
of
motion.
The
Washita
Valley
fault
is
the
largest
fault
in
the
area,
with
a
surface
trace
of
approximately
56
km
(Tanner,
1967).
It
is
a
major
fault
that
is
known
to
extend
nearly
180
km
from
the
Ouachita
thrust
system
in
the
southeast
to
the
Anadarko
basin
to
the
northwest
(Tanner,
1967).
Estimates
for
the
amount
of
left-­‐lateral
strike-­‐slip
accommodated
on
this
fault
vary
dramatically,
but
reasonably
range
from
65
km
(Tanner,
1967)
to
26
km
(McCaskill,
1998).
The
Roberson
fault,
to
south
of
the
Washita
Valley
fault,
is
a
thrust
fault
with
an
associated
overturned
syncline
with
significant
shortening
(Swesnick
and
Green,
1950).
The
Reagan,
Eola
and
Mill
Creek
faults
as
mapped
by
Harlton
(1964)
all
show
significant
components
of
left
lateral
strike
slip
(Granath,
1989).
The
Eola
field
contains
several
fault
blocks
in
between
these
major
faults,
with
all
the
faults
in
the
subsurface
having
near
vertical
dips
(Harlton,
1964).
To
the
southeast
of
the
Eola
Field
is
the
highly
faulted
West
Timbered
Hills
of
the
northwestern
Arbuckle
Mountains
(Harlton,
1964).
The
Eola
Field
was
discovered
in
1947
with
a
discovery
well
completed
to
a
total
depth
of
10,234
feet
(3,119
m)
in
the
basal
Bromide
Sandstone.
The
initial
bottom
hole
pressure
was
about
3800
PSI
and
by
1950
had
declined
to
2,900
PSI
with
seven
producing
wells
in
the
field
(Swesnick
and
Green,
1950).
4
Figure
2
-­‐
Fault
map
for
the
Eola
Field,
Oklahoma.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
Faults
shown
as
thin
grey
lines
are
from
Stoeser
et
al.
(2007).
Eola
field
is
colored
a
salmon
color
(Boyd,
2002).
Hydraulic
Fracturing
Operations
at
Picket
Unit
B
Well
4-­‐18
Hydraulic
fracturing
operations
began
on
Monday
January
17,
2011
at
approximately
6
AM
(CST),
12:00
UTC.
The
hydraulic
fracturing
of
the
well
consisted
of
a
four-­‐stage
hydraulic
fracturing
operation
with
frac
intervals
of
9,830’-­‐
10,282’,
8,890’-­‐8326’,
7,662’-­‐8,128’,
and
7,000’-­‐7,562’,
with
the
last
frac
stage
completed
on
January
23,
2011.
The
well
was
then
flushed
until
February
6,
2011.
Because
the
earthquakes
began
after
the
first
frac
stage
we
will
primarily
consider
this
stage.
The
first
frac
stage
had
an
average
rate
of
injection
of
88.5
bpm
and
an
average
injection
pressure
of
4850
psi.
This
stage
also
included
an
acid
stimulation.
There
was
a
total
of
2,475,545
gallons
of
frac
fluid
injected
and
575,974
lbs
of
propent.
The
Picket
Unit
B
well
4-­‐18
is
a
nearly
vertical
well
located
at
34.55272
-­‐
97.44580,
elevation
277.4
m,
with
an
API
number
of
049-­‐24797.
The
first
frac
occurred
in
the
interval
beteween
9,830’
(2,996.2
m),
and
10,282’
(3,134.0
m)
Earthquake
Data
Analysis
and
Methods
The
Garvin
County,
earthquakes
were
analyzed
using
routine
processing
steps
by
the
OGS
for
earthquake
monitoring.
The
phase
arrivals
were
picked
using
the
interactive
picking
capabilities
of
the
seismic
software
package
SEISAN
(Havskov
and
Ottemoller,
1999).
The
earthquake
hypocenters
and
origin
times
were
determined
using
the
location
program
HYPOCENTER
(Lienert
et
al.,
1986
and
Lienert
and
Havskov,
1995).
The
OGS
typical
duration
magnitude
calculations
were
Garvin
Carter
Eola Fault
Reagan Fault
Mill Creek Fault
Roberson Fault
Washita Valley Fault
97°20'0"W
97°20'0"W
97°30'0"W
97°30'0"W
34°40'0"N 34°40'0"N
34°30'0"N 34°30'0"N
0 2 4 8 12 16
Kilometers
5
used
to
determine
the
magnitude
of
the
earthquakes
(Lawson
and
Luza,
2006).
The
velocity
model
used
is
the
same
model
that
is
currently
being
used
by
the
OGS
for
most
regions
of
Oklahoma,
the
���Manitou
Model”
shown
in
Table
1.
Using
the
HYPOELLIPSE
method
hypocenter
locations
are
poorly
resolved
because
the
nearest
station
is
approximately
35
km
away,
phase
arrivals
were
difficult
to
identify
for
these
events,
and
the
events
appear
to
have
been
shallow.
The
formal
uncertainties
are
significant
in
the
range
of
several
kilometers
for
these
earthquakes
and
indicate
that
locations
for
these
earthquakes
should
be
considered
suspect.
The
formal
error
estimates
from
the
initial
HYPOCENTER
locations
can
be
seen
in
Table
2.
Aside
from
the
formal
uncertainties
it
is
very
likely
that
the
regional
velocity
model
used
is
not
quite
appropriate
for
this
area
of
Oklahoma.
In
fact,
a
single
velocity
model
is
definitely
not
appropriate
across
the
structurally
complex
region
spanning
the
deep
(>10km)
Ardmore
basin
to
the
immediately
adjacent
Arbuckle
uplift.
In
an
attempt
to
improve
the
hypocenter
determinations
the
Double-­‐Differencing,
HypoDD,
technique
of
Waldhauser
and
Ellsworth
(2000)
was
employed
to
relocate
the
earthquakes.
This
approach
takes
advantage
of
the
fact
that
there
is
very
little
difference
in
phase
traveltimes
between
earthquakes
that
occur
near
each
other.
It
can
then
use
all
the
earthquakes
to
find
the
centroid
of
the
earthquakes,
while
more
easily
identifying
and
excluding
bad
phase
arrival
times
at
stations.
Once
the
centroid
of
the
earthquakes
is
determined
the
relative
location
of
each
earthquake
to
the
centroid
can
accurately
be
determined.
HypoDD
provides
very
good
resolution
of
relative
earthquake
locations,
but
the
absolute
earthquake
location
error
can
be
larger
than
the
formal
error
estimates.
The
singular
value
decomposition
(SVD)
method
was
used
in
HypoDD
because
this
is
a
small
dataset,
and
the
SVD
method
provides
a
better
estimate
of
the
formal
uncertainties
(Waldhauser,
2001).
HypoDD
also
has
the
capability
to
use
waveform
cross
correlation
between
events.
Waveform
cross-­‐correlations
can
often
dramatically
improve
earthquake
hypocentral
location
errors,
by
removing
any
human
error
in
phase
arrival
picks.
This
method
uses
the
similarities
in
waveforms
between
events
to
more
accurately
measure
arrival
times,
and
has
been
shown
to
dramatically
improve
locations
and
their
associated
uncertainties.
Cross
correlation
is
simply
finding
the
part
of
the
recorded
waveform,
which
is
most
like
the
template
waveform
window.
A
template
waveform
window
is
an
example
waveform
around
either
a
P
or
S-­‐Wave
arrival
from
an
event
within
the
earthquake
sequence.
Cross
correlations
for
these
earthquakes
were
attempted.
In
order
to
attempt
the
cross
correlation
a
few
of
the
larger
events
were
selected
as
templates
and
windows
around
the
P
and
S
phase
arrivals
were
selected.
These
windows
where
then
run
against
the
corresponding
template
event
to
determine
how
well
the
data
could
be
cross-­‐correlated
with
the
entire
waveform
for
the
respective
earthquake.
In
this
test,
the
S-­‐waves
could
readily
be
identified
using
cross
correlation,
but
the
P-­‐wave
could
not.
The
P-­‐waves
were
generally
correlating
better
with
S
or
surface
waves
in
the
coda
than
with
the
P
phase
arrival,
except
for
two
stations
X34A
and
Y34A.
The
inability
to
cross-­‐
6
Table
1
-­‐
Velocity
models
used
in
this
study;
all
have
a
Vp/Vs
ratio
of
1.73.
Manitou
and
Chelsea
models
are
derived
from
Mitchell
and
Landisman
(1970).
Tryggvason
and
Qualls
(1967)
model
was
developed
from
the
same
seismic
refraction
line
as
Mitchell
and
Landisman
(1970).
The
Central
Oklahoma
model
was
developed
from
traveltime
inversion
for
earthquakes
in
central
Oklahoma.
Chelsea
Central
Oklahoma
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
0.6
4.00
2.31
0.5
4.46
2.58
0.4
6.05
3.50
0.5
4.60
2.66
2.1
5.50
3.18
2.0
4.75
2.75
10.3
6.08
3.51
0.5
6.13
3.54
3.0
6.49
3.75
1.5
6.16
3.56
1.5
6.20
3.58
3.0
6.19
3.58
8.2
6.72
3.88
2.0
6.19
3.58
9.1
7.05
4.08
5.0
6.20
3.58
11.1
7.36
4.25
11.0
6.73
3.89
half-­‐space
8.18
4.73
9.0
7.10
4.11
11.0
7.36
4.25
half-­‐space
8.18
4.73
Ma
nitou
Tryggva
son-­‐Qualls
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
1.0
5.50
3.18
0.54
4.00
2.31
9.5
6.08
3.51
13.16
5.96
3.45
5.1
6.49
3.75
15.90
6.66
3.85
2.5
6.20
3.58
21.84
7.20
4.16
8.2
6.72
3.88
half-­‐space
8.32
4.81
9.1
7.05
4.08
11.1
7.36
4.25
half-­‐space
8.18
4.73
7
Table
2
–
Initial
hypocenter
locations
from
SEISAN
and
HYPOCENTER.
Large
uncertainties
in
hypocentral
locations
are
typical
of
earthquakes
without
nearby
seismic
stations.
The
mean
error
at
a
90%
confidence
interval
in
locations
is
3.8,
5.2,
14.4
km
for
longitude,
latitude,
depth
respectively.
8
correlate
an
earthquake’s
P-­‐Wave
arrival
with
the
template,
excluded
the
possibility
of
using
cross-­‐correlation
data
for
earthquake
relocations
using
HypoDD.
Because
the
events
are
shallow,
the
hypocentral
depths
were
fixed
to
2.5
km
to
prevent
events
that
were
initially
located
at
the
surface
from
being
excluded
immediately
in
the
relocation
process.
In
order
to
address
the
sensitivity
to
velocity
models,
relocations
were
conducted
for
all
velocity
models
listed
in
Table
1.
Only
the
velocity
model
varied
between
HypoDD
relocations
for
the
different
velocity
models.
These
models
all
correspond
reasonably
well
and
earthquakes
hypocenters
moved
well
away
from
the
initial
2.5
km
depth
imposed
on
the
input
data.
A
comparison
of
cluster
locations
is
shown
in
Table
3
and
Figure
3.
The
model
selected
to
represent
the
results
of
the
relocations
is
the
Chelsea
model.
This
model
is
consistent
with
all
the
others.
Its
cluster
centroid
while
a
little
shallower
than
the
other
models
is
centrally
located
and
retained
the
most
earthquakes
in
the
relocation
process.
The
mean
2σ
error
is
164.7,
274.8,
362.4
meters
for
x
(longitude),
y
(latitude),
and
z
(depth)
respectively.
The
final
hypocenter
relocations
can
be
seen
in
Table
4
and
Figure
4.
As
mentioned
earlier
the
uncertainties
provided
by
HypoDD
provide
good
relative
estimates.
In
order
to
address
what
the
absolute
uncertainties
might
be,
we
examined
the
maximum
distance
between
all
of
the
cluster
centroids
and
the
Chelsea
model
cluster
centroid
from
Table
3.
The
greatest
distances
in
cluster
centroid
from
that
of
the
Chelsea
centroid
are
160
m
in
longitude,
115
m
in
latitude,
and
264
m
in
depth.
Our
absolute
error
could
be
considered
the
addition
of
the
previous
values
to
the
relative
locations
uncertainties
in
Table
4.
The
total
earthquake
location
uncertainties
are
shown
in
Figure
11b.
A
value
for
the
Vp/Vs
ratio
of
1.73
was
used
in
all
of
the
relocations.
Because
the
locations
of
these
earthquakes
rely
on
the
high
quality
S-­‐
Wave
phase
arrivals
this
value
can
have
a
significant
impact
on
the
relocations
of
these
events.
An
evaluation
of
the
appropriate
Vp/Vs
ratio
is
well
beyond
the
scope
of
this
work
and
may
be
evaluated
in
the
future.
The
uncertainties
should
be
considered
a
minimum
for
the
earthquake
relocations
given
our
assumption
of
the
Vp/Vs
ratio
and
the
lack
of
nearby
stations.
9
Table
3
–
HypoDD
relocation
cluster
centroids
for
the
different
velocity
models
used.
The
number
of
earthquakes
that
remained
in
the
solution
is
shown
in
the
last
column.
HypoDD
eliminates
earthquakes
that
occur
above
the
surface
or
lose
link
to
nearby
earthquakes
in
the
cluster.
!"#$% &'()(*#$ &"+,)(*#$ -$.(/01234
5$),/($#0
6!7
8*39$:0";0
<':(/=*'2$>
!"#$%&' ()*+),),- .,/*)0)0/1 0*/-)(2+ 3*00-( (/
456786" ()*++3+(( .,/*)0)01- 0*),,-2) 3*02 )(
9:;<<="88.
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46#%:"7?
@A7"5&B" ()*++2(1) .,/*)0(,12 0*+(+)/2 3*03,) )0
Figure
3
–
HypoDD
cluster
centroid
locations,
black
crosses,
in
relationship
to
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
is
shown
in
salmon.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
TQ
COK
Chelsea
Manitou
97°25'0"W
97°25'0"W
97°26'0"W
97°26'0"W
97°27'0"W
97°27'0"W
34°33'0"N 34°33'0"N
34°32'0"N 34°32'0"N
0 0.2 0.4 0.8 1.2 1.6
Kilometers
10
Figure
4
–
HypoDD
earthquake
relocations
(colored
by
depth
in
kilometers)
determined
using
Chelsea
model.
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
shown
cross-­‐hachured
area.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
97°22'0"W
97°22'0"W
97°24'0"W
97°24'0"W
97°26'0"W
97°26'0"W
97°28'0"W
97°28'0"W
34°34'0"N 34°34'0"N
34°32'0"N 34°32'0"N
0 0.5 1 2 3 4
Kilometers
Legend
Chelsea Model
Depth
0.77 - 1.45
1.46 - 2.12
2.13 - 2.68
2.69 - 3.64
3.65 - 5.62
11
Table
4
–
HypoDD
relocations
using
the
Chelsea
velocity
model.
The
mean
2σ
error
is
164.7,
274.8,
362.4
meters
for
longitude,
latitude,
depth
respectively.
!"#$#%&' !()*$#%&'
+',#-.
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344(4.
!()./12
344(4.
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344(4.
+',#-.
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7
8 +5 96
7
: ;3< 7&
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!"#$"(&!, '(") ,#,) ,*+#+ ,($#) )()#$ )*,, , )) ,$ + "(#"+ )
12
Summary
of
Earthquake
Activity
The
earthquake
activity
in
southern
Garvin
County
began
at
1/17/11
19:19
UTC
and
there
were
43
earthquakes
large
enough
to
be
located
by
1/19/11
4:29
UTC.
Of
these
events,
39
earthquakes
occurred
by
1/18/11
9:52
UTC,
with
largest
having
a
duration
magnitude
of
2.8
(Md)
and
the
smallest
a
Md
1.0.
The
timing
of
these
events
can
be
seen
in
Figures
5
and
6.
The
first
earthquake
began
about
1
hour
and
20
minutes
after
hydraulic-­‐fracturing
operations
had
ceased.
The
earthquakes
exhibited
waveforms
with
an
unusual
character.
A
comparison
of
waveform
recordings
between
one
of
the
larger
earthquakes
in
the
southern
Garvin
County
earthquake
sequence,
that
occurrued
on
January
18th,
and
an
earthquake
that
occurred
a
little
bit
further
north
in
Garvin
county,
on
January
25th,
of
the
same
magnitude
are
shown
in
Figures
7,
8
and
9.
The
unique
character
of
these
events
which
make
them
appear
different
than
other
regionally
recorded
earthquakes
are:
• The
events
are
clearly
shallow
and
generate
significant
surface
wave
energy
• P-­‐waves
are:
– Subdued
in
amplitude
– Not
impulsive
even
on
the
closest
stations
– Significant
energy
in
the
P-­‐coda
(ringing)
– Nearly
as
prominent
on
horizontal
as
vertical
components
– Very
hard
to
identify
on
all
but
the
nearest
seismic
stations
– Could
not
be
identified
using
cross
correlation,
generally
correlating
better
to
an
arrival
sometime
after
the
S-­‐wave
• S-­‐waves
are:
– Somewhat
difficult
to
distinguish
from
P-­‐coda
and
because
of
the
significant
surface
wave
energy
– Easiest
phase
to
identify
on
most
seismic
stations
– Identifiable
using
cross
correlation
as
well
These
characteristics
definitely
suggest
that
the
shallow
hypocenter
locations
are
most
likely
not
an
artifact
of
the
location
algorithm
(program)
or
velocity
model.
Any
other
conclusions
about
the
unique
character
of
these
events
would
be
speculative.
The
earthquakes
occur
within
the
portion
of
the
Eola
field,
which
has
many
small
fault
bounded
blocks.
The
seismicity
appears
consistent
with
activation
on
portions
of
these
fault
bounding
blocks
or
smaller
faults
within
the
blocks.
Due
to
the
character
of
the
P-­‐wave
arrivals
it
was
not
possible
to
produce
first
motion
focal
mechanisms
for
these
earthquakes.
The
majority
of
the
earthquakes
occur
within
4
km
horizontal
distance
from
the
Picket
Unit
B
well.
13
Figure
5
–
Time
magnitude
plot
of
Eola
Field
earthquakes
following
hydraulic
fracturing
at
Picket
Unit
B
Well
4-­‐18.
Hydraulic
fracturing
began
at
about
1/17/11
12:00.
14
Figure
6
–
HypoDD
relocations
using
the
Chelsea
velocity
model;
symbols
are
colored
by
the
number
of
hours
after
the
first
earthquake
observed
in
the
Eola
Field.
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
shown
cross-­‐
hachured
area.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
97°22'0"W
97°22'0"W
97°24'0"W
97°24'0"W
97°26'0"W
97°26'0"W
97°28'0"W
97°28'0"W
34°34'0"N 34°34'0"N
34°32'0"N 34°32'0"N
0 0.5 1 2 3 4
Kilometers
Legend
Chelsea Model
Time
0.0 - 3.0
3.1 - 9.3
9.4 - 17.1
17.2 - 32.9
33.0 - 115.4
15
Figure
7
–
Comparison
of
two
similar
sized
earthequakes
recorded
at
station
X34A
in
Garvin
County.
The
earthquake
on
Jan.
18
occurred
in
the
Enola
Field
and
the
earthquake
on
Jan
25
occurred
further
to
the
north
at
about
the
same
epicentral
distance.
The
waveforms
are
aligned
on
each
events
corresponding
origin
time.
Vertical
Radial
X34A Transverse
Jan 18 00:14
M2.6, 37 km
Jan 25 08:48
Md2.6, 36 km
Seconds
16
Figure
8
–
Comparison
of
two
similar
sized
earthequakes
recorded
at
station
X34A
in
Garvin
County.
The
earthquake
on
Jan.
18
occurred
in
the
Enola
Field
and
the
earthquake
on
Jan
25
occurred
further
to
the
north.
The
waveforms
are
aligned
on
each
events
corresponding
origin
time.
Vertical
Radial
X35A Transverse
Jan 18 00:14
Md2.6, 46 km
Jan 25 08:48
Md2.6, 57 km
Seconds
17
Figure
9
–
Comparison
of
P-­‐Wave
arrivals
for
the
two
events
compared
in
Figures
7
and
8.
P-­‐waves
for
the
Jan.
18th
Eola
Field
earthquake
have
lower
frequency
arrivals
than
those
from
the
earthquake
on
Jan.
25th.
18
Discussion
Anthropogenic
triggered
seismicity
has
regained
scientific
and
media
attention
recently.
Recent
earthquakes
in
the
Dallas-­‐Fort
Worth
area
(Frohlich
et
al.,
2011)
and
earthquakes
near
Guy,
Arkansas,
have
dramatically
raised
this
issue
to
some
significance.
Cases
of
clear
anthropogenically-­‐triggered
seismicity
from
fluid
injection
are
well
documented
with
correlations
between
the
number
of
earthquakes
in
an
area
and
injection,
specifically
injection
pressures,
with
earthquakes
occurring
very
close
to
the
well.
Examples
of
clearly
induced
seismicity
include
the
Rocky
Mountain
Arsenal
(Hsieh
and
Bredehoeft,
1981),
Rangely,
Colorado
(Raleigh
et
al.,
1972;
Raleigh
et
al.,
1976),
Paradox
Valley,
Colorado
(Ake
et
al.,
2005),
and
the
KTB
Deep
Well
in
Germany
(Jost
et
al.,
1995;
Baisch
et
al.,
2002).
There
are
also
many
examples
from
enhanced
geothermal
systems
where
there
is
a
clear
correlation
between
injection
and
earthquakes.
Examples
of
these
include,
but
are
not
limited
to
Frenton
Hill,
New
Mexico
(Fehler
et
al.,
1998),
Basel,
Switzerland
(Deichmann
and
Giardini,
2009),
Cooper
Basin,
Australia
(Baisch
et
al.,
2006),
and
Soultz,
France
(Horalek
et
al.,
2010).
Figure
10
demonstrates
the
earthquake
distribution
as
a
function
of
distance
from
the
well
for
a
few
of
these
cases.
In
the
cases
from
Rangely,
Colorado
and
the
Rocky
Mountain
Arsenal
the
majority
of
seismicity
lies
within
a
distance
of
4
km
from
the
injection
well,
which
is
quite
comparable
to
what
is
seen
for
the
Picket
Unit
B
well
in
this
study.
There
are
also
less
clear
examples
in
which
earthquakes
may
or
may
not
have
been
triggered
by
fluid
injection
at
a
well.
In
these
cases,
there
is
no
clear
correlation
between
fluid
injection
and
earthquakes
and
the
earthquakes
may
occur
at
somewhat
larger
distances
from
the
suspected
wells.
Some
examples
of
these
cases
are
Sleepy
Hollow
Oil
Field,
Nebraska
(Rothe
and
Lui,
1983;
Evans
and
Steeples,
1987);
a
gas
field,
Lacq
France
(Grasso
and
Wittlinger,
1990);
a
deep
waste
disposal
well
in
northeastern
Ohio
(Nicholson
et
al.,
1988;
Seeber
et
al.,
2004);
Fashing,
Texas
(Davis
et
al.,
1995);
the
Wabash
Valley,
Illinois
(Eager
et
al.,
2006),
and
the
DFW
airport
(Frohlich
et
al.,
2011).
These
are
not
exhaustive
lists
of
proposed
induced
seismicity
and
there
is
a
large
spectrum
of
scientific
opinions
regarding
many
of
these
cases.
19
Figure
10
–
Number
of
earthquakes
verses
distance
for
selected
examples
where
seismicity
is
clearly
induced
from
fluid
injection
at
depth.
The
information
was
hand
digitized
from
Raleigh
et
al.
(1972),
Hsieh
and
Bredehoeft
(1981),
and
Baisch
et
al.
(2002).
The
bin
size
used
is
0.25
km.
20
Figure
11
–
a)
Number
of
earthquakes
plotted
versus
distance
from
the
Picket
Unit
B
Well
4-­‐18.
Total
and
vertical
distances
were
determined
relative
to
the
central
depth
of
hydraulic
fracturing
stage
1.
b)
Spatial
distribution
of
earthquakes
in
relationship
to
Well
4-­‐18
with
estimated
absolute
location
error
shown
as
green
crosses.
The
depth
interval
for
the
first
frac
stage
is
shown
as
the
crimson
portion
of
the
well.
a)
b)
Well 4-18
21
Davis
and
Frolich
(1993)
outlined
seven
questions
to
help
aid
in
examining
whether
or
not
earthquakes
may
have
been
induced
by
fluid
injection
at
depth.
We
will
examine
these
seven
questions
in
relation
to
the
hydraulic
fracturing
of
the
Picket
Unit
B
and
the
earthquakes
observed
in
the
Eola
Field
in
Garvin
County.
Affirmative
answers
to
all
seven
questions
according
to
Frolich
and
Davis
(1993)
would
indicate
that
earthquakes
are
clearly
induced.
Question
1:
Are
these
events
the
first
known
earthquakes
of
this
character
in
the
region?
(UNKOWN)
Given
the
analog
recording
history
for
most
of
the
Oklahoma
Geological
Survey’s
recording
history
it
is
difficult
to
determine
whether
the
character
is
uniquely
different
from
that
of
earthquakes
previously
observed
in
the
area.
There
have
been
significant
numbers
of
earthquakes
occurring
in
this
area
in
the
past,
Figure
1.
This
negative
response
by
itself
would
suggest
that
hydro-­‐fracturing
at
Picket
Unit
B
did
not
induce
these
earthquakes.
However,
we
will
examine
all
of
the
criteria
outlined
by
Davis
and
Frolich
(1993).
Question
2:
Is
there
a
clear
correlation
between
injection
and
seismicity?
(YES)
There
is
a
clear
correlation
between
the
time
of
hydraulic-­‐fracturing
and
the
observed
seismicity
in
the
Eola
Field.
However,
subsequent
hydraulic-­‐fracturing
stages
at
Picket
Unit
B
Well
4-­‐18
did
not
appear
to
have
any
earthquakes
associated
with
them.
Subsequent
frac
stages
were
all
shallower
than
the
first,
and
otherwise
there
were
no
major
differences
in
the
fracking
operations.
Question
3:
Are
epicenters
near
wells
(within
5
km)?
(YES)
Nearly
all
earthquakes
are
located
within
this
distance
and
the
majority
of
earthquakes
are
closer
than
the
5
km
specified
by
Davis
and
Frolich
(1993).
The
5
km
was
selected
somewhat
arbitrarily
by
Davis
and
Frolich
(1993)
and
may
not
be
completely
appropriate.
The
earthquakes
hypocenters
have
formal
uncertainties
from
HypoDD,
including
our
uncertainty
in
velocity
model,
of
about
320
m
in
longitude
and
490
m
in
latitude.
These
uncertainties
represent
the
absolute
minimum
of
what
we
should
consider
the
location
error
to
be.
Unknown
effects
of
different
Vp/Vs
ratios
and
other
factors
add
to
the
actual
error
in
location
being
larger.
Figure
11
demonstrates
the
distance
of
earthquakes
from
the
well.
Question
4:
Do
some
earthquakes
occur
at
or
near
injection
depths?
(YES)
Most
of
the
earthquakes
do
occur
near
injection
depths.
The
minimum
uncertainty
in
focal
mechanism
depths
should
be
considered
approximately
630
m.
The
focal
depth
is
the
least
well-­‐constrained
portion
of
the
hypocenter
location
and
reported
depths
should
be
considered
somewhat
suspect
since
there
are
no
stations
within
a
few
kilometers
of
the
earthquake
sequence.
The
waveform
characteristics
are
consistent
with
the
shallow
focal
depths
from
the
double-­‐differencing
relocation.
hypocentral
depths
and
formal
uncertainties
can
be
seen
in
Figure
11b.
22
Question
5:
If
not,
are
there
known
geologic
structures,
that
may
channel
flow
to
sites
of
earthquakes?
(YES)
There
are
significant
structures
within
the
Eola
Field.
The
near
vertical
block
bounding
faults
provide
a
pathway
for
fluid
flow
in
the
subsurface.
In
addition
faults
are
rarely
single
entities
but
rather
a
complex
network
of
faults
and
fractures
increasing
the
number
of
structures
that
could
potentially
channel
flow
(Scholz,
1990).
The
average
error
in
depth
should
be
considered
to
be
at
a
minimum
630
m
and
should
be
expected
to
be
larger
since
there
are
no
nearby
stations
to
help
constrain
the
focal
depth.
Question
6:
Are
changes
in
fluid
pressure
at
well
bottoms
sufficient
to
encourage
seismicity?
(YES)
Clearly
since
the
case
considered
here
involves
hydraulic-­‐fracturing
where
pressure
is
being
used
to
fracture
rock,
by
design
the
pressures
are
sufficient
to
encourage
seismicity.
Question
7:
Are
changes
in
fluid
pressure
at
hypocentral
locations
sufficient
to
encourage
seismicity?
(UNKNOWN)
A
further
examination
of
this
question
is
provided
below.
It
is
possible
to
apply
a
reasonable
physical
model
that
suggests
the
hydraulic
fracturing
could
have
increased
pressures
at
hypocentral
locations.
With
all
the
production
that
has
occurred
within
the
Eola
Field
and
our
uncertainty
in
subsurface
structure
it
would
be
difficult
if
not
impossible
to
accurately
model
the
effects
of
a
pressure
pulse
at
hypocentral
locations.
This
is
especially
true
given
the
uncertainties
in
earthquake
locations
in
this
study.
After
having
evaluated
the
above
criteria
we
have
five
affirmative
responses
and
two
uncertain
responses.
Is
this
enough
to
determine
that
these
earthquakes
were
triggered
or
not?
At
this
point
I
would
like
to
directly
quote
Davis
and
Frolich
(1993).
“At
present
it
is
impossible
to
predict
the
effects
of
injection
with
absolute
certainty.
This
uncertainty
arises
both
because
the
underlying
physical
mechanisms
of
earthquakes
are
poorly
understood,
and
because
in
nearly
every
specific
situation
there
is
inadequate
or
incomplete
information
about
regional
stresses,
fluid
migration,
historical
seismicity,
etc.
Clearly,
a
series
of
seven
or
ten
yes
or
no
questions
oversimplifies
many
of
these
issues.”
This
statement
reflects
the
incredible
complexity
and
uncertainty
for
most
cases
in
associating
anthropogenic
causes
and
earthquakes.
The
physical
mechanism,
which
could
trigger
these
earthquakes
from
the
hydraulic
fracturing
operations
at
the
Picket
Unit
B
well,
is
the
diffusion
of
pore-­‐pressure
interacting
with
a
pre-­‐existing
structure
to
initiate
earthquakes
on
a
fault
or
fracture
that
has
an
orientation
favorable
to
failure
within
the
regional
stress
field.
Many
researchers
have
described
the
migration
of
induced
seismicity
by
describing
the
migration
of
a
pressure
front
through
the
diffusion
of
pore
pressure,
hydraulic
23
diffusivity
(Talwani
and
Acree,
1985;
Nicholson
and
Wesson,
1990;
Shapiro
et
al.,
1999;
Rothert
and
Shapiro,
2003;
Rozhko,
2010).
Cornet
(2000)
argued
that
the
shape
of
microseismicity
is
controlled
by
the
fracture
process
and
hydromechanical
coupling
rather
than
a
homogeneous
hydraulic
diffusivity
through
a
rock
mass.
Rutledge
et
al.
(2004)
describe
this
behavior
in
detail
for
a
closely
monitored
hydraulic
fracturing
within
the
Carthage
Cotton
Valley
Gas
Field,
Texas.
They
clearly
demonstrate
the
control
of
the
regional
stress
field,
pressure
diffusion,
inter-­‐
action
with
existing
structures
and
suggest
that
there
is
a
significant
amount
of
aseismic
slip
occurring
within
the
fractured
volume.
In
order
to
examine
whether
or
not
the
data
for
this
earthquake
sequence
would
fit
a
pore
pressure
diffusion
model
we
used
the
simplified
pore
pressure
diffusion
model
of
Talwani
and
Acree
(1985).
This
method
describes
the
pore
pressure
diffusion
through
time
through
via
a
diffusion
constant
called
seismic
hydraulic
diffusivity.
This
hydraulic
diffusivity
can
be
related
to
the
physical
properties
of
the
rocks
and
fluids
involved
such
as
fluid
viscosity,
rock
porosity
and
permeability,
and
the
compressibility
of
the
fluid
and
rocks.
There
is
a
simple
method
to
determine
the
seismic
hydraulic
diffusivity
(α),
! =
!!
!
where
L
is
the
distance
of
the
earthquake
away
from
the
well
in
centimeters
(cm)
and
t
is
the
time,
in
seconds,
since
injection
began.
Talwani
and
Acree
(1985)
found
that
seismic
hydraulic
diffusivity
for
the
cases
they
examined
ranged
from
5x103
to
6x105
cm2/s.
For
our
case
we
determined
the
seismic
hydraulic
diffusivity
which
fit
95%
of
the
earthquakes
was
2.8x106
to
2.6x106cm2/s
depending
on
whether
this
was
determined
for
the
total
hypocentral
distance
from
the
center
point
of
the
injection
interval
or
simply
the
radial
distance
from
the
well.
The
hydraulic
diffusivity
can
be
related
to
permeability
from
the
following
relationship.
! =
!
!"!!
where,
k
–
is
the
permeability
μ – is the viscosity of water (10-8 bar/s)
ϕ – is the porosity of fractured rock (3x10-3 for this example, and
βF = is the effective compressibility of the fluid (3x10-5 bar-1).
This
provides
a
maximum
permeability
needed
to
describe
this
earthquake
sequence
of
255
milliDarcies
(mD).
In
this
example
the
uncertainties
in
earthquake
locations
are
not
considered
(Figure
12).
While
this
permeability
may
seem
high
for
a
shale
it
is
within
the
values
reported
for
in
situ
rocks,
especially
fractured
rock
(Brace,
1984).
24
Figure
12
–
a)
Pore
pressure
diffusion
model
results
shown
for
total
distance
from
Picket
Unit
B
Well
4-­‐18.
Red
crosses
show
earthquake
locations
relative
to
the
midpoint
of
the
first
hydraulic
fracturing
stage,
and
the
solid
black
line
represents
location
at
a
specific
time
of
the
pore
pressure
front
from
the
model.
Earthquakes
plotted
above
this
line
are
inconsistent
with
this
pore
pressure
diffusion
model,
and
all
earthquakes
plotted
below
this
line
are
consistent
with
this
pore
pressure
diffusion
model.
This
line
represents
a
seismic
hydraulic
diffusivity
of
2.8x106
cm2/s,
which
is
roughly
equivalent
to
a
permeability
of
255
milliDarcies
(mD),
and
represents
the
distance
from
the
well
of
a
pressure
front.
b)
Same
as
for
(a)
except
only
the
radial
distance
is
considered.
The
resultant
seismic
hydraulic
diffusivity
is
2.6x106cm2/s.
25
Conclusions
Determining
whether
or
not
earthquakes
have
been
induced
in
most
portions
of
the
stable
continent
is
problematic,
because
of
our
poor
knowledge
of
historical
earthquakes,
earthquake
processes
and
the
long
recurrence
intervals
for
earthquakes
in
the
stable
continent.
In
addition
understanding
fluid
flow
and
pressure
diffusion
in
the
unique
geology
and
structures
of
an
area
poses
real
and
significant
challenges.
The
strong
spatial
and
temporal
correlations
to
the
hydraulic-­‐fracturing
in
Picket
Unit
B
Well
4-­‐18
certainly
suggest
that
the
earthquakes
observed
in
the
Eola
Field
could
have
possibly
been
triggered
by
this
activity.
Simply
because
the
earthquakes
fit
a
simple
pore
pressure
diffusion
model
does
not
indicate
that
this
is
the
physical
process
that
caused
these
earthquakes.
The
number
of
historical
earthquakes
in
the
area
and
uncertainties
in
hypocenter
locations
make
it
impossible
to
determine
with
a
high
degree
of
certainty
whether
or
not
hydraulic-­‐fracturing
induced
these
earthquakes.
Whether
or
not
the
earthquakes
in
the
Eola
Field
were
triggered
by
hydraulic-­‐
fracturing
these
were
small
earthquakes
with
only
one
local
resident
having
reported
feeling
them.
While
the
societal
impact
of
understanding
whether
or
not
small
earthquakes
may
have
been
caused
by
hydraulic-­‐fracturing
may
be
small,
it
could
potentially
help
us
learn
more
about
subsurface
properties
such
as
stresses
at
depth,
strength
of
faults,
fluid
flow,
pressure
diffusion,
and
long
term
fault
and
earthquake
behaviors
of
the
stable
continent.
It
may
also
be
possible
to
identify
what
criteria
may
affect
the
likelihood
of
anthropogenically
induced
earthquakes
and
provide
oil
and
gas
operators
the
ability
to
minimize
any
adverse
affects
as
suggested
by
Shapiro
et
al.
(2007).
Acknowledgements
The
NSF
Earthscope
Project
and
the
Transportable
Array
stations
and
data
availability
provided
by
IRIS
made
this
work
possible.
I
would
also
like
to
thank
Amie
Gibson,
Dr.
Kenneth
V.
Luza,
and
Dr.
G.
Randal
Keller
for
their
helpful
comments
and
suggestions
for
this
paper.
Russell
Standbridge,
OGS
Cartography,
provided
a
great
deal
of
technical
advice
and
information.
I
would
also
like
to
thank
the
Oklahoma
Corporation
Commission
for
the
help
in
obtaining
information
and
input
to
this
effort.
I
would
also
like
to
thank
Cimarex
Energy
Co.
for
providing
usefull
technical
information
about
the
hydraulic
fracturing
of
Picket
Unit
B
Well
4-­‐
18.
26
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Amer.,
96(5),
p.
1718-­‐1728.
Evans,
D.G.
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D.W.
Steeples,
1987,
Microearthquakes
near
the
Sleepy
Hollow
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Southwestern
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Bull.
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Amer.,
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p.
132-­‐140.
Fehler,
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L.
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W.S.
Phillips,
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Potter,
1998,
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travel-­‐time
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microearthquakes
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189-­‐201.
Frohlich,
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2011,
The
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327-­‐340.
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Earthquakes
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784-­‐798.
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J.W.,
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Structural
Evolution
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1015-­‐1036.
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Harlton,
B.H.,
1964,
Tectonic
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Oil
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West
Timbered
Hills
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Murray
Counties,
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Ottemoller,
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SeisAn
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Horalek,
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2010,
Source
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micro-­‐earthquakes
induced
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site
Soultz-­‐sous-­‐Forets
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in
2003
and
their
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spatial
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A
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903-­‐
920.
Jost, M.L., T. BuBelberg, O. Jost, H.P. Harjes,1995, Source Parameters of Injection-
Induced Microearthquakes at 9 km Depth at the KTB Deep Drilling Site,
Germany, Bull. Seismol. Soc. Amer., 88(3), p. 815-822.
Keller, G.R., E.G. Lidiak, W.J. Hinze, and L.W. Braile, 1983, The Role of Rifting in the
Tectonic Development of the Midcontinent, U.S.A., Tectonophysics, 94, p. 391-
412.
Lawson,
J.E.
Jr.
and
K.V.
Luza,
2006,
Oklahoma
Earthquakes
2005,
Oklahoma
Geology
Notes,
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66,
No.
3,
Fall
2006.
Lienert,
B.
R.
E.,
E.
Berg,
and
L.N.
Frazer,
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Hypocenter:
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centered,
scaled,
and
adaptively
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Bull.
Seismol.
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Am.,
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p.
771–783.
Lienert,
B.
R.
E.
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and
globally,
Seismol.
Res.
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p.
26–36.
McCaskill, J.G. Jr., 1998, Multiple Stratigraphic Indicators of Major Strike-Slip
Movement Along the Eola Fault, Subsurface, Arbuckle Mountains, Oklahoma,
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Mitchell, B.J. and M. Landisman, 1970, Interpretation of a Crustal Section across
Oklahoma, Geol. Soc. Amer. Bul., 81(9), p. 2647-2656.
Nicholson, C., E. Roeloffs, and R.L. Wesson, 1988, The Northeastern Ohio Earthquake
of 31 January 1986: Was It Induced?, Bull. Seismol. Soc. Amer., 78(1), p. 188-
217.
Nicholson, C. and R.L. Wesson, 1990, Earthquake Hazard Associated With Deep Well
Injection – A Report to the U.S. Environmental Protection Agency, U.S. Geol.
Surv. Bull, 1951, pp. 74.
Northcutt, R.A. and J.A., Campbell, 1995, Geologic provinces of Oklahoma, Oklahoma
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Control at Rangely, Colorado, Science, 191, p. 1230-1237.
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73(5), p. 1357-1367.
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Examination
of
Possibly
Induced
Seismicity
from
Hydraulic
Fracturing
in
the
Eola
Field,
Garvin
County,
Oklahoma
Austin
Holland
Oklahoma
Geological
Survey
Open-­‐File
Report
OF1-­‐2011
OKLAHOMA
GEOLOGICAL
SURVEY
Open-­���file
Report
Disclaimer
This
Open-­‐file
Report
is
intended
to
make
the
results
of
research
available
at
the
earliest
possible
date
and
not
intended
to
represent
the
final
or
formal
publication.
The
report
is
an
unedited
copy
prepared
by
the
author.
Examination
of
Possibly
Induced
Seismicity
from
Hydraulic
Fracturing
in
the
Eola
Field,
Garvin
County,
Oklahoma
Austin
A.
Holland
Oklahoma
Geological
Survey
Sarkeys
Energy
Center
100
East
Boyd
St.,
Rm.
N-­‐131
Norman,
Oklahoma
73019-­‐0628
August
2011
Oklahoma
Geological
Survey
Open-­‐File
Report
OF1-­‐2011
1
Summary
On
January
18,
2011,
The
Oklahoma
Geological
Survey
(OGS)
received
a
phone
call
from
a
resident
living
south
of
Elmore
City,
in
Garvin
County,
Oklahoma,
that
reported
feeling
several
earthquakes
throughout
the
night.
The
reporting
local
resident
had
also
offered
that
there
was
an
active
hydraulic
fracturing
project
occurring
nearby.
Upon
examination
there
were
nearly
50
earthquakes,
which
occurred
during
that
time.
After
analyzing
the
data
there
were
43
earthquakes
large
enough
to
be
located,
which
from
the
character
of
the
seismic
recordings
indicate
that
they
are
both
shallow
and
unique.
The
earthquakes
range
in
magnitude
from
1.0
to
2.8
Md
and
the
majority
of
earthquakes
occurred
within
about
24
hours
of
the
first
earthquake.
Careful
attention
and
significant
effort
was
put
into
obtaining
the
most
accurate
locations
possible
and
gaining
a
reasonable
estimate
in
the
error
in
locations.
The
nearest
seismic
station
is
35
km
away
from
where
the
earthquakes
occurred.
Formal
errors
in
location
are
on
the
order
100-­‐500
m
horizontally
and
about
twice
that
for
depth.
Examination
of
different
velocity
models
would
suggest
that
the
uncertainties
in
earthquake
locations
should
be
about
twice
the
formal
uncertainties.
The
majority
of
earthquakes
appear
to
have
occurred
within
about
3.5
km
of
the
well
located
in
the
Eola
Field
of
southern
Garvin
County.
The
Eola
Field
has
many
structures,
which
may
provide
conduits
for
fluid
flow
at
depth.
The
well
is
Picket
Unit
B
well
4-­‐18,
and
about
seven
hours
after
the
first
and
deepest
hydraulic
fracturing
stage
started
the
earthquakes
began
occurring.
It
was
possible
to
model
95%
of
the
earthquakes
in
this
sequence
using
a
simple
pore
pressure
diffusion
model
with
a
permeability
of
about
250
mD
(milliDarcies).
While
this
permeability
may
be
high
it
is
less
than
those
reported
for
highly
fractured
rock.
The
strong
correlation
in
time
and
space
as
well
as
a
reasonable
fit
to
a
physical
model
suggest
that
there
is
a
possibility
these
earthquakes
were
induced
by
hydraulic-­‐fracturing.
However,
the
uncertainties
in
the
data
make
it
impossible
to
say
with
a
high
degree
of
certainty
whether
or
not
these
earthquakes
were
triggered
by
natural
means
or
by
the
nearby
hydraulic-­‐fracturing
operation.
Introduction
On
January
18th,
2011,
a
resident
living
in
south-­‐central
Oklahoma
(Garvin
County),
living
south
of
Elmore
City
contacted
the
Oklahoma
Geological
Survey
(OGS)
to
report
feeling
several
earthquakes
throughout
the
night
with
the
first
occurring
at
approximately
6:10
PM
CST
Jan.
17th
and
another
large
one
at
about
2:50
AM
CST
Jan.
18th.
Upon
examination
there
were
in
fact
earthquakes
in
the
area.
The
resident
also
reported
that
there
was
an
active
hydraulic
fracturing
project
being
conducted
in
a
nearby
well.
Examination
of
the
available
seismic
data,
including
EarthScope
USArray
stations
in
the
region,
quickly
confirmed
that
earthquakes
were
occurring
in
the
area.
At
this
point
the
OGS
contacted
the
Regional
Manager
for
the
Oklahoma
Corporation
Commission,
who
indicated
that
there
was
indeed
fracturing
occurring
at
the
Picket
Unit
B
Well
4-­‐18.
Our
analysis
showed
that
shortly
after
hydraulic
fracturing
began
small
earthquakes
started
occurring,
and
more
than
50
were
identified,
of
which
43
were
large
enough
to
be
located.
Most
of
these
earthquakes
2
occurred
within
a
24-­‐hour
period
after
hydraulic
fracturing
operations
had
ceased.
There
have
been
previous
cases
where
seismologists
have
suggested
a
link
between
hydraulic
fracturing
and
earthquakes,
but
data
was
limited,
so
drawing
a
definitive
conclusions
was
not
possible
for
these
cases.
The
first
case
occurred
in
June1978
in
Carter
and
Love
Counties,
just
south
of
Garvin
County,
with
70
earthquakes
in
6.2
hours.
The
second
case
occurred
in
Love
County
with
90
earthquakes
following
the
first
and
second
hydraulic
fracturing
stages
(Nicholson
and
Wesson,
1990).
Figure
1
-­‐
Earthquakes
from
1897-­‐2010
from
the
OGS
catalog
(red
crosses).
Yellow
triangles
are
seismic
stations
from
the
Earthscope
Transportable
Array;
tan
triangles
are
OGS
seismic
stations.
Faults
are
shown
by
thin
black
lines,
solid
are
faults
mapped
from
a
surface
expression,
dotted
lines
indicate
subsurface
faults
(Northcutt
and
Campbell,
1995).
The
main
movement
on
all
of
these
faults
was
in
the
Pennsylvanian
(Granath,
1989).
Hachured
region
shows
the
location
of
the
Eola
Oil
Field
(Boyd,
2002).
South-­‐central
Oklahoma
has
a
significant
amount
of
historical
seismicity,
and
has
been
one
of
the
most
active
areas
within
Oklahoma
since
1977,
when
an
adequate
seismic
network
was
established.
The
nearest
stations
to
the
earthquakes
were
several
Earthscope
Transportable
Array
(TA)
stations.
Without
the
TA
stations
only
Grady
Carter
Garvin
Love
Stephens
Jefferson
Caddo
McClain
Pontotoc
Murray
Cleveland Pottawatomie
Johnston
Marshall
Seminole
Cotton
Comanche
Canadian Oklahoma
Bryan
Okfuskee
FNO
Y35A
Y34A
X35A
X34A
W35A
W34A
96°45'0"W
96°45'0"W
97°0'0"W
97°0'0"W
97°15'0"W
97°15'0"W
97°30'0"W
97°30'0"W
97°45'0"W
97°45'0"W
98°0'0"W
98°0'0"W
98°15'0"W
98°15'0"W
35°15'0"N 35°15'0"N
35°0'0"N 35°0'0"N
34°45'0"N 34°45'0"N
34°30'0"N 34°30'0"N
34°15'0"N 34°15'0"N
34°0'0"N 34°0'0"N
33°45'0"N 33°45'0"N
0 4 8 16 24 32
Kilometers
3
a
few
of
the
earthquakes
could
possibly
have
been
located
and
the
uncertainties
in
the
hypocentral
locations
would
be
quite
large.
Geologic
Setting
The
Eola
Field
lies
at
the
northern
edge
of
the
Ardmore
Basin
and
the
buried
northwestern
extent
of
the
Arbuckle
Mountains
and
contains
a
highly
folded
and
faulted
thrust
system
(Swesnick
and
Green,
1950;
Harlton,
1964,
Granath,
1989).
In
the
Cambrian
this
area
experienced
significant
rifting
associated
with
the
Southern
Oklahoma
aulacogen
(Keller
et
al.,
1983).
After
the
initial
rifting
the
area
experienced
thermal
subsidence
and
sedimentation
(Granath,
1989).
The
area
continued
to
see
periods
of
subsidence
and
sedimentation
with
a
few
periods
of
erosion
represented
by
unconformities
(Swesnik
and
Green,
1950).
In
the
mid-­‐
Pennsylvanian
the
area
began
to
experience
significant
transpression
associated
with
the
Ouachita
Orogen
(Granath,
1989).
Because
of
the
areas
complex
tectonic
history
it
is
quite
likely
that
the
nature
of
faults
has
changed
through
time
and
that
normal
faults
associated
with
the
aulacogen
and
later
basin
accommodation
were
reactivated
in
the
mid
to
late-­‐Pennsylvanian
with
a
new
sense
of
motion.
The
Washita
Valley
fault
is
the
largest
fault
in
the
area,
with
a
surface
trace
of
approximately
56
km
(Tanner,
1967).
It
is
a
major
fault
that
is
known
to
extend
nearly
180
km
from
the
Ouachita
thrust
system
in
the
southeast
to
the
Anadarko
basin
to
the
northwest
(Tanner,
1967).
Estimates
for
the
amount
of
left-­‐lateral
strike-­‐slip
accommodated
on
this
fault
vary
dramatically,
but
reasonably
range
from
65
km
(Tanner,
1967)
to
26
km
(McCaskill,
1998).
The
Roberson
fault,
to
south
of
the
Washita
Valley
fault,
is
a
thrust
fault
with
an
associated
overturned
syncline
with
significant
shortening
(Swesnick
and
Green,
1950).
The
Reagan,
Eola
and
Mill
Creek
faults
as
mapped
by
Harlton
(1964)
all
show
significant
components
of
left
lateral
strike
slip
(Granath,
1989).
The
Eola
field
contains
several
fault
blocks
in
between
these
major
faults,
with
all
the
faults
in
the
subsurface
having
near
vertical
dips
(Harlton,
1964).
To
the
southeast
of
the
Eola
Field
is
the
highly
faulted
West
Timbered
Hills
of
the
northwestern
Arbuckle
Mountains
(Harlton,
1964).
The
Eola
Field
was
discovered
in
1947
with
a
discovery
well
completed
to
a
total
depth
of
10,234
feet
(3,119
m)
in
the
basal
Bromide
Sandstone.
The
initial
bottom
hole
pressure
was
about
3800
PSI
and
by
1950
had
declined
to
2,900
PSI
with
seven
producing
wells
in
the
field
(Swesnick
and
Green,
1950).
4
Figure
2
-­‐
Fault
map
for
the
Eola
Field,
Oklahoma.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
Faults
shown
as
thin
grey
lines
are
from
Stoeser
et
al.
(2007).
Eola
field
is
colored
a
salmon
color
(Boyd,
2002).
Hydraulic
Fracturing
Operations
at
Picket
Unit
B
Well
4-­‐18
Hydraulic
fracturing
operations
began
on
Monday
January
17,
2011
at
approximately
6
AM
(CST),
12:00
UTC.
The
hydraulic
fracturing
of
the
well
consisted
of
a
four-­‐stage
hydraulic
fracturing
operation
with
frac
intervals
of
9,830’-­‐
10,282’,
8,890’-­‐8326’,
7,662’-­‐8,128’,
and
7,000’-­‐7,562’,
with
the
last
frac
stage
completed
on
January
23,
2011.
The
well
was
then
flushed
until
February
6,
2011.
Because
the
earthquakes
began
after
the
first
frac
stage
we
will
primarily
consider
this
stage.
The
first
frac
stage
had
an
average
rate
of
injection
of
88.5
bpm
and
an
average
injection
pressure
of
4850
psi.
This
stage
also
included
an
acid
stimulation.
There
was
a
total
of
2,475,545
gallons
of
frac
fluid
injected
and
575,974
lbs
of
propent.
The
Picket
Unit
B
well
4-­‐18
is
a
nearly
vertical
well
located
at
34.55272
-­‐
97.44580,
elevation
277.4
m,
with
an
API
number
of
049-­‐24797.
The
first
frac
occurred
in
the
interval
beteween
9,830’
(2,996.2
m),
and
10,282’
(3,134.0
m)
Earthquake
Data
Analysis
and
Methods
The
Garvin
County,
earthquakes
were
analyzed
using
routine
processing
steps
by
the
OGS
for
earthquake
monitoring.
The
phase
arrivals
were
picked
using
the
interactive
picking
capabilities
of
the
seismic
software
package
SEISAN
(Havskov
and
Ottemoller,
1999).
The
earthquake
hypocenters
and
origin
times
were
determined
using
the
location
program
HYPOCENTER
(Lienert
et
al.,
1986
and
Lienert
and
Havskov,
1995).
The
OGS
typical
duration
magnitude
calculations
were
Garvin
Carter
Eola Fault
Reagan Fault
Mill Creek Fault
Roberson Fault
Washita Valley Fault
97°20'0"W
97°20'0"W
97°30'0"W
97°30'0"W
34°40'0"N 34°40'0"N
34°30'0"N 34°30'0"N
0 2 4 8 12 16
Kilometers
5
used
to
determine
the
magnitude
of
the
earthquakes
(Lawson
and
Luza,
2006).
The
velocity
model
used
is
the
same
model
that
is
currently
being
used
by
the
OGS
for
most
regions
of
Oklahoma,
the
���Manitou
Model”
shown
in
Table
1.
Using
the
HYPOELLIPSE
method
hypocenter
locations
are
poorly
resolved
because
the
nearest
station
is
approximately
35
km
away,
phase
arrivals
were
difficult
to
identify
for
these
events,
and
the
events
appear
to
have
been
shallow.
The
formal
uncertainties
are
significant
in
the
range
of
several
kilometers
for
these
earthquakes
and
indicate
that
locations
for
these
earthquakes
should
be
considered
suspect.
The
formal
error
estimates
from
the
initial
HYPOCENTER
locations
can
be
seen
in
Table
2.
Aside
from
the
formal
uncertainties
it
is
very
likely
that
the
regional
velocity
model
used
is
not
quite
appropriate
for
this
area
of
Oklahoma.
In
fact,
a
single
velocity
model
is
definitely
not
appropriate
across
the
structurally
complex
region
spanning
the
deep
(>10km)
Ardmore
basin
to
the
immediately
adjacent
Arbuckle
uplift.
In
an
attempt
to
improve
the
hypocenter
determinations
the
Double-­‐Differencing,
HypoDD,
technique
of
Waldhauser
and
Ellsworth
(2000)
was
employed
to
relocate
the
earthquakes.
This
approach
takes
advantage
of
the
fact
that
there
is
very
little
difference
in
phase
traveltimes
between
earthquakes
that
occur
near
each
other.
It
can
then
use
all
the
earthquakes
to
find
the
centroid
of
the
earthquakes,
while
more
easily
identifying
and
excluding
bad
phase
arrival
times
at
stations.
Once
the
centroid
of
the
earthquakes
is
determined
the
relative
location
of
each
earthquake
to
the
centroid
can
accurately
be
determined.
HypoDD
provides
very
good
resolution
of
relative
earthquake
locations,
but
the
absolute
earthquake
location
error
can
be
larger
than
the
formal
error
estimates.
The
singular
value
decomposition
(SVD)
method
was
used
in
HypoDD
because
this
is
a
small
dataset,
and
the
SVD
method
provides
a
better
estimate
of
the
formal
uncertainties
(Waldhauser,
2001).
HypoDD
also
has
the
capability
to
use
waveform
cross
correlation
between
events.
Waveform
cross-­‐correlations
can
often
dramatically
improve
earthquake
hypocentral
location
errors,
by
removing
any
human
error
in
phase
arrival
picks.
This
method
uses
the
similarities
in
waveforms
between
events
to
more
accurately
measure
arrival
times,
and
has
been
shown
to
dramatically
improve
locations
and
their
associated
uncertainties.
Cross
correlation
is
simply
finding
the
part
of
the
recorded
waveform,
which
is
most
like
the
template
waveform
window.
A
template
waveform
window
is
an
example
waveform
around
either
a
P
or
S-­‐Wave
arrival
from
an
event
within
the
earthquake
sequence.
Cross
correlations
for
these
earthquakes
were
attempted.
In
order
to
attempt
the
cross
correlation
a
few
of
the
larger
events
were
selected
as
templates
and
windows
around
the
P
and
S
phase
arrivals
were
selected.
These
windows
where
then
run
against
the
corresponding
template
event
to
determine
how
well
the
data
could
be
cross-­‐correlated
with
the
entire
waveform
for
the
respective
earthquake.
In
this
test,
the
S-­‐waves
could
readily
be
identified
using
cross
correlation,
but
the
P-­‐wave
could
not.
The
P-­‐waves
were
generally
correlating
better
with
S
or
surface
waves
in
the
coda
than
with
the
P
phase
arrival,
except
for
two
stations
X34A
and
Y34A.
The
inability
to
cross-­‐
6
Table
1
-­‐
Velocity
models
used
in
this
study;
all
have
a
Vp/Vs
ratio
of
1.73.
Manitou
and
Chelsea
models
are
derived
from
Mitchell
and
Landisman
(1970).
Tryggvason
and
Qualls
(1967)
model
was
developed
from
the
same
seismic
refraction
line
as
Mitchell
and
Landisman
(1970).
The
Central
Oklahoma
model
was
developed
from
traveltime
inversion
for
earthquakes
in
central
Oklahoma.
Chelsea
Central
Oklahoma
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
0.6
4.00
2.31
0.5
4.46
2.58
0.4
6.05
3.50
0.5
4.60
2.66
2.1
5.50
3.18
2.0
4.75
2.75
10.3
6.08
3.51
0.5
6.13
3.54
3.0
6.49
3.75
1.5
6.16
3.56
1.5
6.20
3.58
3.0
6.19
3.58
8.2
6.72
3.88
2.0
6.19
3.58
9.1
7.05
4.08
5.0
6.20
3.58
11.1
7.36
4.25
11.0
6.73
3.89
half-­‐space
8.18
4.73
9.0
7.10
4.11
11.0
7.36
4.25
half-­‐space
8.18
4.73
Ma
nitou
Tryggva
son-­‐Qualls
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
Thickness
(km)
Vp
(km/s)
Vs
(km/s)
1.0
5.50
3.18
0.54
4.00
2.31
9.5
6.08
3.51
13.16
5.96
3.45
5.1
6.49
3.75
15.90
6.66
3.85
2.5
6.20
3.58
21.84
7.20
4.16
8.2
6.72
3.88
half-­‐space
8.32
4.81
9.1
7.05
4.08
11.1
7.36
4.25
half-­‐space
8.18
4.73
7
Table
2
–
Initial
hypocenter
locations
from
SEISAN
and
HYPOCENTER.
Large
uncertainties
in
hypocentral
locations
are
typical
of
earthquakes
without
nearby
seismic
stations.
The
mean
error
at
a
90%
confidence
interval
in
locations
is
3.8,
5.2,
14.4
km
for
longitude,
latitude,
depth
respectively.
8
correlate
an
earthquake’s
P-­‐Wave
arrival
with
the
template,
excluded
the
possibility
of
using
cross-­‐correlation
data
for
earthquake
relocations
using
HypoDD.
Because
the
events
are
shallow,
the
hypocentral
depths
were
fixed
to
2.5
km
to
prevent
events
that
were
initially
located
at
the
surface
from
being
excluded
immediately
in
the
relocation
process.
In
order
to
address
the
sensitivity
to
velocity
models,
relocations
were
conducted
for
all
velocity
models
listed
in
Table
1.
Only
the
velocity
model
varied
between
HypoDD
relocations
for
the
different
velocity
models.
These
models
all
correspond
reasonably
well
and
earthquakes
hypocenters
moved
well
away
from
the
initial
2.5
km
depth
imposed
on
the
input
data.
A
comparison
of
cluster
locations
is
shown
in
Table
3
and
Figure
3.
The
model
selected
to
represent
the
results
of
the
relocations
is
the
Chelsea
model.
This
model
is
consistent
with
all
the
others.
Its
cluster
centroid
while
a
little
shallower
than
the
other
models
is
centrally
located
and
retained
the
most
earthquakes
in
the
relocation
process.
The
mean
2σ
error
is
164.7,
274.8,
362.4
meters
for
x
(longitude),
y
(latitude),
and
z
(depth)
respectively.
The
final
hypocenter
relocations
can
be
seen
in
Table
4
and
Figure
4.
As
mentioned
earlier
the
uncertainties
provided
by
HypoDD
provide
good
relative
estimates.
In
order
to
address
what
the
absolute
uncertainties
might
be,
we
examined
the
maximum
distance
between
all
of
the
cluster
centroids
and
the
Chelsea
model
cluster
centroid
from
Table
3.
The
greatest
distances
in
cluster
centroid
from
that
of
the
Chelsea
centroid
are
160
m
in
longitude,
115
m
in
latitude,
and
264
m
in
depth.
Our
absolute
error
could
be
considered
the
addition
of
the
previous
values
to
the
relative
locations
uncertainties
in
Table
4.
The
total
earthquake
location
uncertainties
are
shown
in
Figure
11b.
A
value
for
the
Vp/Vs
ratio
of
1.73
was
used
in
all
of
the
relocations.
Because
the
locations
of
these
earthquakes
rely
on
the
high
quality
S-­‐
Wave
phase
arrivals
this
value
can
have
a
significant
impact
on
the
relocations
of
these
events.
An
evaluation
of
the
appropriate
Vp/Vs
ratio
is
well
beyond
the
scope
of
this
work
and
may
be
evaluated
in
the
future.
The
uncertainties
should
be
considered
a
minimum
for
the
earthquake
relocations
given
our
assumption
of
the
Vp/Vs
ratio
and
the
lack
of
nearby
stations.
9
Table
3
–
HypoDD
relocation
cluster
centroids
for
the
different
velocity
models
used.
The
number
of
earthquakes
that
remained
in
the
solution
is
shown
in
the
last
column.
HypoDD
eliminates
earthquakes
that
occur
above
the
surface
or
lose
link
to
nearby
earthquakes
in
the
cluster.
!"#$% &'()(*#$ &"+,)(*#$ -$.(/01234
5$),/($#0
6!7
8*39$:0";0
!"#$%&' ()*+),),- .,/*)0)0/1 0*/-)(2+ 3*00-( (/
456786" ()*++3+(( .,/*)0)01- 0*),,-2) 3*02 )(
9:;<<="88.
>'"778 ()*+),,/- .,/*)0-30+ 0*-,+,+/ 3*00( (+
46#%:"7?
@A7"5&B" ()*++2(1) .,/*)0(,12 0*+(+)/2 3*03,) )0
Figure
3
–
HypoDD
cluster
centroid
locations,
black
crosses,
in
relationship
to
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
is
shown
in
salmon.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
TQ
COK
Chelsea
Manitou
97°25'0"W
97°25'0"W
97°26'0"W
97°26'0"W
97°27'0"W
97°27'0"W
34°33'0"N 34°33'0"N
34°32'0"N 34°32'0"N
0 0.2 0.4 0.8 1.2 1.6
Kilometers
10
Figure
4
–
HypoDD
earthquake
relocations
(colored
by
depth
in
kilometers)
determined
using
Chelsea
model.
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
shown
cross-­‐hachured
area.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
97°22'0"W
97°22'0"W
97°24'0"W
97°24'0"W
97°26'0"W
97°26'0"W
97°28'0"W
97°28'0"W
34°34'0"N 34°34'0"N
34°32'0"N 34°32'0"N
0 0.5 1 2 3 4
Kilometers
Legend
Chelsea Model
Depth
0.77 - 1.45
1.46 - 2.12
2.13 - 2.68
2.69 - 3.64
3.65 - 5.62
11
Table
4
–
HypoDD
relocations
using
the
Chelsea
velocity
model.
The
mean
2σ
error
is
164.7,
274.8,
362.4
meters
for
longitude,
latitude,
depth
respectively.
!"#$#%&' !()*$#%&'
+',#-.
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344(4.
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344(4.
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7
8 +5 96
7
: ;3< 7&
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12
Summary
of
Earthquake
Activity
The
earthquake
activity
in
southern
Garvin
County
began
at
1/17/11
19:19
UTC
and
there
were
43
earthquakes
large
enough
to
be
located
by
1/19/11
4:29
UTC.
Of
these
events,
39
earthquakes
occurred
by
1/18/11
9:52
UTC,
with
largest
having
a
duration
magnitude
of
2.8
(Md)
and
the
smallest
a
Md
1.0.
The
timing
of
these
events
can
be
seen
in
Figures
5
and
6.
The
first
earthquake
began
about
1
hour
and
20
minutes
after
hydraulic-­‐fracturing
operations
had
ceased.
The
earthquakes
exhibited
waveforms
with
an
unusual
character.
A
comparison
of
waveform
recordings
between
one
of
the
larger
earthquakes
in
the
southern
Garvin
County
earthquake
sequence,
that
occurrued
on
January
18th,
and
an
earthquake
that
occurred
a
little
bit
further
north
in
Garvin
county,
on
January
25th,
of
the
same
magnitude
are
shown
in
Figures
7,
8
and
9.
The
unique
character
of
these
events
which
make
them
appear
different
than
other
regionally
recorded
earthquakes
are:
• The
events
are
clearly
shallow
and
generate
significant
surface
wave
energy
• P-­‐waves
are:
– Subdued
in
amplitude
– Not
impulsive
even
on
the
closest
stations
– Significant
energy
in
the
P-­‐coda
(ringing)
– Nearly
as
prominent
on
horizontal
as
vertical
components
– Very
hard
to
identify
on
all
but
the
nearest
seismic
stations
– Could
not
be
identified
using
cross
correlation,
generally
correlating
better
to
an
arrival
sometime
after
the
S-­‐wave
• S-­‐waves
are:
– Somewhat
difficult
to
distinguish
from
P-­‐coda
and
because
of
the
significant
surface
wave
energy
– Easiest
phase
to
identify
on
most
seismic
stations
– Identifiable
using
cross
correlation
as
well
These
characteristics
definitely
suggest
that
the
shallow
hypocenter
locations
are
most
likely
not
an
artifact
of
the
location
algorithm
(program)
or
velocity
model.
Any
other
conclusions
about
the
unique
character
of
these
events
would
be
speculative.
The
earthquakes
occur
within
the
portion
of
the
Eola
field,
which
has
many
small
fault
bounded
blocks.
The
seismicity
appears
consistent
with
activation
on
portions
of
these
fault
bounding
blocks
or
smaller
faults
within
the
blocks.
Due
to
the
character
of
the
P-­‐wave
arrivals
it
was
not
possible
to
produce
first
motion
focal
mechanisms
for
these
earthquakes.
The
majority
of
the
earthquakes
occur
within
4
km
horizontal
distance
from
the
Picket
Unit
B
well.
13
Figure
5
–
Time
magnitude
plot
of
Eola
Field
earthquakes
following
hydraulic
fracturing
at
Picket
Unit
B
Well
4-­‐18.
Hydraulic
fracturing
began
at
about
1/17/11
12:00.
14
Figure
6
–
HypoDD
relocations
using
the
Chelsea
velocity
model;
symbols
are
colored
by
the
number
of
hours
after
the
first
earthquake
observed
in
the
Eola
Field.
Picket
Unit
B
Well
4-­‐18,
shown
as
black
hexagon,
Eola
Field
(Boyd,
2002)
shown
cross-­‐
hachured
area.
Thick
green
lines
are
faults
modified
from
Harlton
(1964).
97°22'0"W
97°22'0"W
97°24'0"W
97°24'0"W
97°26'0"W
97°26'0"W
97°28'0"W
97°28'0"W
34°34'0"N 34°34'0"N
34°32'0"N 34°32'0"N
0 0.5 1 2 3 4
Kilometers
Legend
Chelsea Model
Time
0.0 - 3.0
3.1 - 9.3
9.4 - 17.1
17.2 - 32.9
33.0 - 115.4
15
Figure
7
–
Comparison
of
two
similar
sized
earthequakes
recorded
at
station
X34A
in
Garvin
County.
The
earthquake
on
Jan.
18
occurred
in
the
Enola
Field
and
the
earthquake
on
Jan
25
occurred
further
to
the
north
at
about
the
same
epicentral
distance.
The
waveforms
are
aligned
on
each
events
corresponding
origin
time.
Vertical
Radial
X34A Transverse
Jan 18 00:14
M2.6, 37 km
Jan 25 08:48
Md2.6, 36 km
Seconds
16
Figure
8
–
Comparison
of
two
similar
sized
earthequakes
recorded
at
station
X34A
in
Garvin
County.
The
earthquake
on
Jan.
18
occurred
in
the
Enola
Field
and
the
earthquake
on
Jan
25
occurred
further
to
the
north.
The
waveforms
are
aligned
on
each
events
corresponding
origin
time.
Vertical
Radial
X35A Transverse
Jan 18 00:14
Md2.6, 46 km
Jan 25 08:48
Md2.6, 57 km
Seconds
17
Figure
9
–
Comparison
of
P-­‐Wave
arrivals
for
the
two
events
compared
in
Figures
7
and
8.
P-­‐waves
for
the
Jan.
18th
Eola
Field
earthquake
have
lower
frequency
arrivals
than
those
from
the
earthquake
on
Jan.
25th.
18
Discussion
Anthropogenic
triggered
seismicity
has
regained
scientific
and
media
attention
recently.
Recent
earthquakes
in
the
Dallas-­‐Fort
Worth
area
(Frohlich
et
al.,
2011)
and
earthquakes
near
Guy,
Arkansas,
have
dramatically
raised
this
issue
to
some
significance.
Cases
of
clear
anthropogenically-­‐triggered
seismicity
from
fluid
injection
are
well
documented
with
correlations
between
the
number
of
earthquakes
in
an
area
and
injection,
specifically
injection
pressures,
with
earthquakes
occurring
very
close
to
the
well.
Examples
of
clearly
induced
seismicity
include
the
Rocky
Mountain
Arsenal
(Hsieh
and
Bredehoeft,
1981),
Rangely,
Colorado
(Raleigh
et
al.,
1972;
Raleigh
et
al.,
1976),
Paradox
Valley,
Colorado
(Ake
et
al.,
2005),
and
the
KTB
Deep
Well
in
Germany
(Jost
et
al.,
1995;
Baisch
et
al.,
2002).
There
are
also
many
examples
from
enhanced
geothermal
systems
where
there
is
a
clear
correlation
between
injection
and
earthquakes.
Examples
of
these
include,
but
are
not
limited
to
Frenton
Hill,
New
Mexico
(Fehler
et
al.,
1998),
Basel,
Switzerland
(Deichmann
and
Giardini,
2009),
Cooper
Basin,
Australia
(Baisch
et
al.,
2006),
and
Soultz,
France
(Horalek
et
al.,
2010).
Figure
10
demonstrates
the
earthquake
distribution
as
a
function
of
distance
from
the
well
for
a
few
of
these
cases.
In
the
cases
from
Rangely,
Colorado
and
the
Rocky
Mountain
Arsenal
the
majority
of
seismicity
lies
within
a
distance
of
4
km
from
the
injection
well,
which
is
quite
comparable
to
what
is
seen
for
the
Picket
Unit
B
well
in
this
study.
There
are
also
less
clear
examples
in
which
earthquakes
may
or
may
not
have
been
triggered
by
fluid
injection
at
a
well.
In
these
cases,
there
is
no
clear
correlation
between
fluid
injection
and
earthquakes
and
the
earthquakes
may
occur
at
somewhat
larger
distances
from
the
suspected
wells.
Some
examples
of
these
cases
are
Sleepy
Hollow
Oil
Field,
Nebraska
(Rothe
and
Lui,
1983;
Evans
and
Steeples,
1987);
a
gas
field,
Lacq
France
(Grasso
and
Wittlinger,
1990);
a
deep
waste
disposal
well
in
northeastern
Ohio
(Nicholson
et
al.,
1988;
Seeber
et
al.,
2004);
Fashing,
Texas
(Davis
et
al.,
1995);
the
Wabash
Valley,
Illinois
(Eager
et
al.,
2006),
and
the
DFW
airport
(Frohlich
et
al.,
2011).
These
are
not
exhaustive
lists
of
proposed
induced
seismicity
and
there
is
a
large
spectrum
of
scientific
opinions
regarding
many
of
these
cases.
19
Figure
10
–
Number
of
earthquakes
verses
distance
for
selected
examples
where
seismicity
is
clearly
induced
from
fluid
injection
at
depth.
The
information
was
hand
digitized
from
Raleigh
et
al.
(1972),
Hsieh
and
Bredehoeft
(1981),
and
Baisch
et
al.
(2002).
The
bin
size
used
is
0.25
km.
20
Figure
11
–
a)
Number
of
earthquakes
plotted
versus
distance
from
the
Picket
Unit
B
Well
4-­‐18.
Total
and
vertical
distances
were
determined
relative
to
the
central
depth
of
hydraulic
fracturing
stage
1.
b)
Spatial
distribution
of
earthquakes
in
relationship
to
Well
4-­‐18
with
estimated
absolute
location
error
shown
as
green
crosses.
The
depth
interval
for
the
first
frac
stage
is
shown
as
the
crimson
portion
of
the
well.
a)
b)
Well 4-18
21
Davis
and
Frolich
(1993)
outlined
seven
questions
to
help
aid
in
examining
whether
or
not
earthquakes
may
have
been
induced
by
fluid
injection
at
depth.
We
will
examine
these
seven
questions
in
relation
to
the
hydraulic
fracturing
of
the
Picket
Unit
B
and
the
earthquakes
observed
in
the
Eola
Field
in
Garvin
County.
Affirmative
answers
to
all
seven
questions
according
to
Frolich
and
Davis
(1993)
would
indicate
that
earthquakes
are
clearly
induced.
Question
1:
Are
these
events
the
first
known
earthquakes
of
this
character
in
the
region?
(UNKOWN)
Given
the
analog
recording
history
for
most
of
the
Oklahoma
Geological
Survey’s
recording
history
it
is
difficult
to
determine
whether
the
character
is
uniquely
different
from
that
of
earthquakes
previously
observed
in
the
area.
There
have
been
significant
numbers
of
earthquakes
occurring
in
this
area
in
the
past,
Figure
1.
This
negative
response
by
itself
would
suggest
that
hydro-­‐fracturing
at
Picket
Unit
B
did
not
induce
these
earthquakes.
However,
we
will
examine
all
of
the
criteria
outlined
by
Davis
and
Frolich
(1993).
Question
2:
Is
there
a
clear
correlation
between
injection
and
seismicity?
(YES)
There
is
a
clear
correlation
between
the
time
of
hydraulic-­‐fracturing
and
the
observed
seismicity
in
the
Eola
Field.
However,
subsequent
hydraulic-­‐fracturing
stages
at
Picket
Unit
B
Well
4-­‐18
did
not
appear
to
have
any
earthquakes
associated
with
them.
Subsequent
frac
stages
were
all
shallower
than
the
first,
and
otherwise
there
were
no
major
differences
in
the
fracking
operations.
Question
3:
Are
epicenters
near
wells
(within
5
km)?
(YES)
Nearly
all
earthquakes
are
located
within
this
distance
and
the
majority
of
earthquakes
are
closer
than
the
5
km
specified
by
Davis
and
Frolich
(1993).
The
5
km
was
selected
somewhat
arbitrarily
by
Davis
and
Frolich
(1993)
and
may
not
be
completely
appropriate.
The
earthquakes
hypocenters
have
formal
uncertainties
from
HypoDD,
including
our
uncertainty
in
velocity
model,
of
about
320
m
in
longitude
and
490
m
in
latitude.
These
uncertainties
represent
the
absolute
minimum
of
what
we
should
consider
the
location
error
to
be.
Unknown
effects
of
different
Vp/Vs
ratios
and
other
factors
add
to
the
actual
error
in
location
being
larger.
Figure
11
demonstrates
the
distance
of
earthquakes
from
the
well.
Question
4:
Do
some
earthquakes
occur
at
or
near
injection
depths?
(YES)
Most
of
the
earthquakes
do
occur
near
injection
depths.
The
minimum
uncertainty
in
focal
mechanism
depths
should
be
considered
approximately
630
m.
The
focal
depth
is
the
least
well-­‐constrained
portion
of
the
hypocenter
location
and
reported
depths
should
be
considered
somewhat
suspect
since
there
are
no
stations
within
a
few
kilometers
of
the
earthquake
sequence.
The
waveform
characteristics
are
consistent
with
the
shallow
focal
depths
from
the
double-­‐differencing
relocation.
hypocentral
depths
and
formal
uncertainties
can
be
seen
in
Figure
11b.
22
Question
5:
If
not,
are
there
known
geologic
structures,
that
may
channel
flow
to
sites
of
earthquakes?
(YES)
There
are
significant
structures
within
the
Eola
Field.
The
near
vertical
block
bounding
faults
provide
a
pathway
for
fluid
flow
in
the
subsurface.
In
addition
faults
are
rarely
single
entities
but
rather
a
complex
network
of
faults
and
fractures
increasing
the
number
of
structures
that
could
potentially
channel
flow
(Scholz,
1990).
The
average
error
in
depth
should
be
considered
to
be
at
a
minimum
630
m
and
should
be
expected
to
be
larger
since
there
are
no
nearby
stations
to
help
constrain
the
focal
depth.
Question
6:
Are
changes
in
fluid
pressure
at
well
bottoms
sufficient
to
encourage
seismicity?
(YES)
Clearly
since
the
case
considered
here
involves
hydraulic-­‐fracturing
where
pressure
is
being
used
to
fracture
rock,
by
design
the
pressures
are
sufficient
to
encourage
seismicity.
Question
7:
Are
changes
in
fluid
pressure
at
hypocentral
locations
sufficient
to
encourage
seismicity?
(UNKNOWN)
A
further
examination
of
this
question
is
provided
below.
It
is
possible
to
apply
a
reasonable
physical
model
that
suggests
the
hydraulic
fracturing
could
have
increased
pressures
at
hypocentral
locations.
With
all
the
production
that
has
occurred
within
the
Eola
Field
and
our
uncertainty
in
subsurface
structure
it
would
be
difficult
if
not
impossible
to
accurately
model
the
effects
of
a
pressure
pulse
at
hypocentral
locations.
This
is
especially
true
given
the
uncertainties
in
earthquake
locations
in
this
study.
After
having
evaluated
the
above
criteria
we
have
five
affirmative
responses
and
two
uncertain
responses.
Is
this
enough
to
determine
that
these
earthquakes
were
triggered
or
not?
At
this
point
I
would
like
to
directly
quote
Davis
and
Frolich
(1993).
“At
present
it
is
impossible
to
predict
the
effects
of
injection
with
absolute
certainty.
This
uncertainty
arises
both
because
the
underlying
physical
mechanisms
of
earthquakes
are
poorly
understood,
and
because
in
nearly
every
specific
situation
there
is
inadequate
or
incomplete
information
about
regional
stresses,
fluid
migration,
historical
seismicity,
etc.
Clearly,
a
series
of
seven
or
ten
yes
or
no
questions
oversimplifies
many
of
these
issues.”
This
statement
reflects
the
incredible
complexity
and
uncertainty
for
most
cases
in
associating
anthropogenic
causes
and
earthquakes.
The
physical
mechanism,
which
could
trigger
these
earthquakes
from
the
hydraulic
fracturing
operations
at
the
Picket
Unit
B
well,
is
the
diffusion
of
pore-­‐pressure
interacting
with
a
pre-­‐existing
structure
to
initiate
earthquakes
on
a
fault
or
fracture
that
has
an
orientation
favorable
to
failure
within
the
regional
stress
field.
Many
researchers
have
described
the
migration
of
induced
seismicity
by
describing
the
migration
of
a
pressure
front
through
the
diffusion
of
pore
pressure,
hydraulic
23
diffusivity
(Talwani
and
Acree,
1985;
Nicholson
and
Wesson,
1990;
Shapiro
et
al.,
1999;
Rothert
and
Shapiro,
2003;
Rozhko,
2010).
Cornet
(2000)
argued
that
the
shape
of
microseismicity
is
controlled
by
the
fracture
process
and
hydromechanical
coupling
rather
than
a
homogeneous
hydraulic
diffusivity
through
a
rock
mass.
Rutledge
et
al.
(2004)
describe
this
behavior
in
detail
for
a
closely
monitored
hydraulic
fracturing
within
the
Carthage
Cotton
Valley
Gas
Field,
Texas.
They
clearly
demonstrate
the
control
of
the
regional
stress
field,
pressure
diffusion,
inter-­‐
action
with
existing
structures
and
suggest
that
there
is
a
significant
amount
of
aseismic
slip
occurring
within
the
fractured
volume.
In
order
to
examine
whether
or
not
the
data
for
this
earthquake
sequence
would
fit
a
pore
pressure
diffusion
model
we
used
the
simplified
pore
pressure
diffusion
model
of
Talwani
and
Acree
(1985).
This
method
describes
the
pore
pressure
diffusion
through
time
through
via
a
diffusion
constant
called
seismic
hydraulic
diffusivity.
This
hydraulic
diffusivity
can
be
related
to
the
physical
properties
of
the
rocks
and
fluids
involved
such
as
fluid
viscosity,
rock
porosity
and
permeability,
and
the
compressibility
of
the
fluid
and
rocks.
There
is
a
simple
method
to
determine
the
seismic
hydraulic
diffusivity
(α),
! =
!!
!
where
L
is
the
distance
of
the
earthquake
away
from
the
well
in
centimeters
(cm)
and
t
is
the
time,
in
seconds,
since
injection
began.
Talwani
and
Acree
(1985)
found
that
seismic
hydraulic
diffusivity
for
the
cases
they
examined
ranged
from
5x103
to
6x105
cm2/s.
For
our
case
we
determined
the
seismic
hydraulic
diffusivity
which
fit
95%
of
the
earthquakes
was
2.8x106
to
2.6x106cm2/s
depending
on
whether
this
was
determined
for
the
total
hypocentral
distance
from
the
center
point
of
the
injection
interval
or
simply
the
radial
distance
from
the
well.
The
hydraulic
diffusivity
can
be
related
to
permeability
from
the
following
relationship.
! =
!
!"!!
where,
k
–
is
the
permeability
μ – is the viscosity of water (10-8 bar/s)
ϕ – is the porosity of fractured rock (3x10-3 for this example, and
βF = is the effective compressibility of the fluid (3x10-5 bar-1).
This
provides
a
maximum
permeability
needed
to
describe
this
earthquake
sequence
of
255
milliDarcies
(mD).
In
this
example
the
uncertainties
in
earthquake
locations
are
not
considered
(Figure
12).
While
this
permeability
may
seem
high
for
a
shale
it
is
within
the
values
reported
for
in
situ
rocks,
especially
fractured
rock
(Brace,
1984).
24
Figure
12
–
a)
Pore
pressure
diffusion
model
results
shown
for
total
distance
from
Picket
Unit
B
Well
4-­‐18.
Red
crosses
show
earthquake
locations
relative
to
the
midpoint
of
the
first
hydraulic
fracturing
stage,
and
the
solid
black
line
represents
location
at
a
specific
time
of
the
pore
pressure
front
from
the
model.
Earthquakes
plotted
above
this
line
are
inconsistent
with
this
pore
pressure
diffusion
model,
and
all
earthquakes
plotted
below
this
line
are
consistent
with
this
pore
pressure
diffusion
model.
This
line
represents
a
seismic
hydraulic
diffusivity
of
2.8x106
cm2/s,
which
is
roughly
equivalent
to
a
permeability
of
255
milliDarcies
(mD),
and
represents
the
distance
from
the
well
of
a
pressure
front.
b)
Same
as
for
(a)
except
only
the
radial
distance
is
considered.
The
resultant
seismic
hydraulic
diffusivity
is
2.6x106cm2/s.
25
Conclusions
Determining
whether
or
not
earthquakes
have
been
induced
in
most
portions
of
the
stable
continent
is
problematic,
because
of
our
poor
knowledge
of
historical
earthquakes,
earthquake
processes
and
the
long
recurrence
intervals
for
earthquakes
in
the
stable
continent.
In
addition
understanding
fluid
flow
and
pressure
diffusion
in
the
unique
geology
and
structures
of
an
area
poses
real
and
significant
challenges.
The
strong
spatial
and
temporal
correlations
to
the
hydraulic-­‐fracturing
in
Picket
Unit
B
Well
4-­‐18
certainly
suggest
that
the
earthquakes
observed
in
the
Eola
Field
could
have
possibly
been
triggered
by
this
activity.
Simply
because
the
earthquakes
fit
a
simple
pore
pressure
diffusion
model
does
not
indicate
that
this
is
the
physical
process
that
caused
these
earthquakes.
The
number
of
historical
earthquakes
in
the
area
and
uncertainties
in
hypocenter
locations
make
it
impossible
to
determine
with
a
high
degree
of
certainty
whether
or
not
hydraulic-­‐fracturing
induced
these
earthquakes.
Whether
or
not
the
earthquakes
in
the
Eola
Field
were
triggered
by
hydraulic-­‐
fracturing
these
were
small
earthquakes
with
only
one
local
resident
having
reported
feeling
them.
While
the
societal
impact
of
understanding
whether
or
not
small
earthquakes
may
have
been
caused
by
hydraulic-­‐fracturing
may
be
small,
it
could
potentially
help
us
learn
more
about
subsurface
properties
such
as
stresses
at
depth,
strength
of
faults,
fluid
flow,
pressure
diffusion,
and
long
term
fault
and
earthquake
behaviors
of
the
stable
continent.
It
may
also
be
possible
to
identify
what
criteria
may
affect
the
likelihood
of
anthropogenically
induced
earthquakes
and
provide
oil
and
gas
operators
the
ability
to
minimize
any
adverse
affects
as
suggested
by
Shapiro
et
al.
(2007).
Acknowledgements
The
NSF
Earthscope
Project
and
the
Transportable
Array
stations
and
data
availability
provided
by
IRIS
made
this
work
possible.
I
would
also
like
to
thank
Amie
Gibson,
Dr.
Kenneth
V.
Luza,
and
Dr.
G.
Randal
Keller
for
their
helpful
comments
and
suggestions
for
this
paper.
Russell
Standbridge,
OGS
Cartography,
provided
a
great
deal
of
technical
advice
and
information.
I
would
also
like
to
thank
the
Oklahoma
Corporation
Commission
for
the
help
in
obtaining
information
and
input
to
this
effort.
I
would
also
like
to
thank
Cimarex
Energy
Co.
for
providing
usefull
technical
information
about
the
hydraulic
fracturing
of
Picket
Unit
B
Well
4-­‐
18.
26
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